nuttx/drivers/1wire/1wire_crc.c

/****************************************************************************
 * drivers/1wire/1wire_crc.c
 *
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.  The
 * ASF licenses this file to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance with the
 * License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
 * License for the specific language governing permissions and limitations
 * under the License.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <stdint.h>
#include <stdbool.h>
#include <string.h>

#include <nuttx/1wire/1wire_crc.h>
#include "1wire_internal.h"

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/* Compute a Dallas Semiconductor 8 bit CRC. */

uint8_t onewire_crc8(FAR const uint8_t *input, uint8_t len)
{
  uint8_t crc = 0;

  while (len-- > 0)
    {
      int i;
      uint8_t inbyte = *input++;

      for (i = 0; i < 8; i++)
        {
          uint8_t mix = (crc ^ inbyte) & 0x01;
          crc >>= 1;
          if (mix)
            crc ^= 0x8c;

          inbyte >>= 1;
        }
    }

  return crc;
}

/* Compute a Dallas Semiconductor 16 bit CRC. This is used to check
 * the integrity of received data from many 1-wire devices.
 *
 * Note: the CRC-16 computed here is not what you'll get from the 1-wire
 * network, because:
 * - The CRC-16 is transmitted bitwise inverted.
 * - The binary representation of the return value may have a different
 *   byte order than the two bytes you get from 1-wire due to endian-ness.
 */

uint16_t onewire_crc16(FAR const uint8_t *input, uint16_t len,
                       uint16_t initial_crc)
{
  uint16_t crc = initial_crc;

  while (len-- > 0)
    {
      int i;
      uint8_t inbyte = *input++;

      for (i = 0; i < 8; i++)
        {
          uint8_t mix = ((crc & 0xff) ^ inbyte) & 0x01;

          crc >>= 1;
          if (mix)
            {
              crc ^= 0xa001;
            }

          inbyte >>= 1;
        }
    }

  return crc;
}

/****************************************************************************
 * Name: onewire_valid_rom
 *
 * Description:
 *   Check CRC-8 of received input
 *
 * Input Parameters:
 *   rom   - 64-bit rom code
 *
 * Returned Value:
 *   true if CRC-8 of rom matches
 *
 ****************************************************************************/

bool onewire_valid_rom(uint64_t rom)
{
  uint8_t crc;
  uint8_t buf[8];

  memcpy(buf, &rom, sizeof(buf));
  crc = onewire_crc8(buf, 7);
  return crc == buf[7];
}

/****************************************************************************
 * Name: onewire_check_crc16
 *
 * Description:
 *   Check CRC-16 of received input
 *
 * Input Parameters:
 *   input         - Array of bytes to checksum
 *   len           - Length of input
 *   inverted_crc  - The two CRC16 bytes in the received data
 *
 * Returned Value:
 *   true if CRC-16 matches
 *
 ****************************************************************************/

bool onewire_check_crc16(FAR const uint8_t *input, uint16_t len,
                         FAR const uint8_t *inverted_crc)
{
  uint16_t crc;

  crc = ~onewire_crc16(input, len, 0);
  return (crc & 0xff) == inverted_crc[0] && (crc >> 8) == inverted_crc[1];
}